Approximately one-half of patients with substance use disorders (SUD) experience chronic pain. Yet how patients perceive the relationship between their substance use and chronic pain remains poorly understood. We sought to identify how patients with comorbid SUD and chronic pain describe the relationship between, and mechanisms linking, these conditions. We conducted qualitative interviews with 34 patients engaged in SUD treatment who were also diagnosed with chronic pain. Interviews were transcribed verbatim and coded by both primary and secondary coders. Qualitative content analysis guided coding and analysis. Patient interviews revealed three primary pathways. One group of participants described SUD as developing independently from their experiences of chronic pain. A second group of participants described turning to substances to self-manage or cope with the physical and emotional aspects of chronic pain. A third group of participants described encounters with opioid medications as the causal agent initiating a SUD. Our findings build upon research that has identified chronic pain and SUD as developmentally similar and mutually reinforcing, by revealing the ways in which patients themselves understand and experience the interconnections between their substance use and chronic pain.